1. Field of the Invention
The present invention relates to a technology for detecting a liquid discharge failure in an inkjet recording apparatus.
2. Description of the Related Art
A typical inkjet recording apparatus includes an inkjet head having minute nozzles that discharge minute ink droplets. The inkjet recording apparatus records an image on a recording medium, such as a sheet of paper, by discharging ink droplets from the inkjet head while relatively moving the inkjet head with respect to the recording medium. The inkjet recording apparatus is widely used because of its advantages including high speed operation, low noise, various types of recording media that can be employed, and ability to perform color printing.
However, the inkjet recording apparatus has drawbacks due to the smallness of the nozzles. For example, the ink in the nozzles easily dries when the recording apparatus is not in operation, dust such as paper dust attaches to the nozzles when they are moist with the ink, or air enters into the nozzles. These drawbacks can cause ink discharge failure. Such ink discharge failure can include non-discharge of the ink, discharge of the ink in a wrong direction, and non-desired size of the ink droplet. As a result, a dead dot or a white line is left on the recording medium, resulting in low image quality.
To overcome such disadvantages, a technology for improving the image quality is disclosed in Japanese Patent Application Laid-open No. 2000-280461. More specifically, a light-emitting element emits a laser light to a light-receiving element in a direction perpendicular to a line on which an inkjet head moves over a recording medium, the inkjet head moves in a main printing direction without any recording medium fed in the inkjet recording apparatus, and the inkjet head discharges an ink droplet toward an optical axis of the laser light. A virtual landing spot is obtained by optically detecting the ink droplet, and a timing of discharging the ink is corrected based on the virtual landing spot.
However, with the technology disclosed in Japanese Patent Application Laid-open No. 2000-280461, only the misalignment of the ink discharge in parallel with the main printing direction can be detected and corrected. In general, a recording error is more visible with the misalignment in parallel with the laser light than the recording error with the misalignment in parallel with the main printing direction, and therefore it is more practical to correct the misalignment in parallel with the laser light.